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Some Geometry Let’s now draw the tangent line l to the circle at point P. We know that l  PO (the tangent line intersects the circle’s radius at a right angle). Hence,  QPO = 90  Copyright  2009 www.biblicalchristianworldview.net

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Derivative Graph Note that when  = 0, then cos  = 1. This means that the slope of the line tangent to the sine curve at 0 is 1. The cosine curve plots that derivative. Copyright  2009 www.biblicalchristianworldview.net

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Derivative Graph When  =  /2, then cos  = 0. This means that the slope of the line tangent to the sine curve at  /2 is 0 (the slope is parallel to the  -axis). Copyright  2009 www.biblicalchristianworldview.net

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Derivative Graph The cosine curve traces the derivative of the sine curve at every point on the sine curve. Copyright  2009 www.biblicalchristianworldview.net